Born in Kyoto, Chushiro Hayashi earned his B.S. in physics at the University of Tokyo in 1942. After World War II he served as a research associate under Hideki Yukawa at Kyoto University, and as an associate professor of physics at Naniwa (now Osaka Prefecture) University. He was at Kyoto University, where he earned his doctorate, from 1954 until his retirement in 1984. In 1950 he made a significant contribution to the αβγ (Alpher-Bethe-Gamow) model of nucleosynthesis in the hot big bang. Hayashi showed that at the high temperatures characteristic of the very early universe, electron-positron pair production had to be taken into account, and this led to revisions in the estimate of the early neutron-proton ratio and a better value for the ultimate abundance of helium in the universe. Hayashi was one of the pioneers in modeling stellar evolution in the 1950s and ’60s. He is best known for his models of star formation and pre-main sequence evolution. Demonstrating that they are fully convective and not in hydrostatic equilibrium, he found that pre-main-sequence stars follow what are now called “Hayashi tracks” downward on the Hertzprung-Russell diagram until they reach the main sequence, i.e., they contract at near-constant surface temperature. Hayashi also worked on the formation of low-mass stars—he and Takenori Nakano made one of the earliest studies of what are now called brown dwarfs—and he investigated the formation of the solar system and of the earth and its atmosphere. He was a leader in building astrophysics in Japan, and some of today’s foremost theorists are his former students. Note: He was also known as Hayashi Chushiro.

Presentation of Bruce medalMercury34, 4, 43 (Jul/Aug 2004). See also the ASP website.